I have a singer heavy duty (model 4423) which ran perfectly well for my purposes until it developed a timing issue about eight months ago.
Fixed the timing issue - developed a feed dog issue.
Fixed the feed dog issue - and now the stitch length adjustment doesn’t work (turn the wheel and nothing happens). I’ve had the casing on and off it five or six times now (so at least I’m getting good at that).
If there’s anyone with a bit of experience fixing up sewing machines who would sit down with me and the machine, and see if it can be saved, I’d really appreciate it. I’m 80% sure it’s something to do with the feed regulating shaft, but the straight stitch cam also doesn’t seem to be behaving itself. I’m properly out of ideas.
The machine is worth less than ithe cost of repair at my local repair shop, which on the bright side means there’s nothing to lose by trying a repair.